(a) Field of the Invention
The present invention relates generally to a coupling structure, and more particularly to a coupling structure which allows insertion therein a tube from one side thereof to be secured therein and permits two adjacent couplings to be positioned at whatever angles.
(b) Description of the Prior Art
Couplings are used to join tubes or pipes at various points and angles so as to form planar or dimensional frameworks for use in tents, for instance. A conventional coupling is shown in FIG. 4. It essentially consists of a sleeve 11 for receiving a circular inner tube 2, and another sleeve 12 welded to the sleeve 11 at a desired angle for receiving another circular tube 2. A screw hole 1" is formed in one side of the sleeves 11, 12 for receiving a bolt 1A such that the bolt 1A may press against one side of the inner tube to position it. However, there are various drawbacks in using such conventional couplings.
1. As the inner tube 2 has to be pushed into the sleeve 11 or 12 from the upper end or the lower end thereof, if the inner tube 2 is long, the operation is quite troublesome and time-consumptive. In particular, if the inner tube 2 is long and slightly curved, it will be difficult to push the inner tube 2 into the sleeve 11 or 12. Likewise, it will be as difficult to remove the inner tube 2 from the sleeve 11 or 12. When erecting a large temporary framework or support which has to be dismantled after use, it will require many skilled workers in order to erect or dismantle the framework within a short time, which is very impractical indeed. PA0 2. After a framework is erected by means of the prior couplings, if it is necessary to install additional tubes at a middle section thereof, since the inner tubes 2 must fit into the sleeves 11 and 12, the entire framework has to be taken apart, which is very time-and labor-consumptive, and uneconomical as well. PA0 3. Since the sleeves 11 and 12 are joined by welding, their angular position cannot be adjusted. If it is required to connect tubes at various angles, a number of couplings 1 of various angles have to be used, so that couplings of various specifications may have to be selected. Besides, there are limited specifications of couplings to allow adjustment of angular connection of the tubes. PA0 4. Since the inner tube 2 is positioned in the sleeve 11 or 12 by means of the bolt 1A which urges against one side of the inner tube 2 from one side of the sleeve 11 or 12, if the inner tube 2 is large or the bolt 1A is not locked tightly, the inner tube 2 may slip out. As a consequence, the framework may easily slant to one side or collapse.